Interpreting Returned Data Pair - Anritsu LMR Master S412E Programming Manual

VNA Commands

Interpreting Returned Data Pair

The following section provides two conversion examples on interpreting returned data pairs.
Examples are provided for both integer and real number formats.
Converting INTeger,32 and REAL,32 Values
• For a 551 point trace, the instrument returns 4415 bytes.
• The first 7 bytes make up the "header" information in ASCI format.
• The next 4408 bytes make up the actual data (8 bytes x 551 datapoints =
4408 total bytes).
• Each datapoint consists of 8 bytes.
• The first 4 bytes are the real component
• The next 4 bytes are the imaginary component.
• The returned value is in little endian format (the little end comes first).
• Negative numbers are represented in two's complement format.
• The data is scaled by a factor of 1e6.
Converting INTeger,32 Example:
The instrument returns the following S11 RL data point in INT,32 format:
4d 15 fc ff [real], ef a2 f8 ff [imag]
1. Convert from little endian to big endian:
ff fc 15 4d [real], ff f8 a2 ef [imag]
2. Since the MSb in both components is 1, they are negative numbers.
3. The binary representation is:
11111111111111000001010101001101 [real], 11111111111110001010001011101111
[imag]
4. Convert from two's complement (not the bits and add 1):
111110101010110011 [real], 1110101110100010001 [imag]
5. Convert the binary values to decimal:
256691 [real], 482577 [imag]
6. Take out the 1e6 scale factor:
0.256691 [real], 0.482577 [imag]
7. Finally, convert the values to dB:
10*log(0.256691^2 + 0.482577^2) = –5.25 dB
S412E PM PN: 10580-00319 Rev. N
5-4 :Format Subsystem
5-41